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61.
The R1 allele confers on potato a race-specific resistance to Phytophthora infestans. The corresponding genetic locus maps on chromosome V in a region in which several other resistance genes are also located. As part of a strategy for cloning R1, a high-resolution genetic map was constructed for the segment of chromosome V that is bordered by the RFLP loci GP21 and GP179 and includes the R1 locus. Bulked segregant analysis and markers based on amplified fragment length polymorphisms (AFLP markers) were used to select molecular markers closely linked to R1. Twenty-nine of approximately 3200 informative AFLP loci displayed linkage to the R1 locus. Based on the genotypic analysis of 461 gametes, eight loci mapped within the GP21–GP179 interval. Two of those could not be seperated from R1 by recombination. For genotyping large numbers of plants with respect to the flanking markers GP21 and GP179 PCR based assays were also developed which allowed marker-assisted selection of plants with genotypes Rr and rr and of recombinant plants.  相似文献   
62.
Treatment with VP-16 (1-50 μM) or excess thymidine (5 mM) caused a block of L cells at different steps in their progression through the replicative cycle. The arrest was followed by an asynchronous process of cell death that conformed to criteria for apoptosis. Careful monitoring of this process in the whole cell population by flow cytometry showed a virtual absence of necrosis, an increase in side light scattering, followed by the occurrence of a population with subdiploid DNA fluorescence as well as reduced forward and side light seattering. The development of apoptosis required sufficient time and adequate ion gradients in the cells. By the combined use of flow cytometry and fluorescence microscopy data were obtained suggesting that (i) intracellular free Ca2+ and pH and/or their drug-induced alterations had to be adequately controlled for the apoptotic process to evolve; (ii) mitochondria were compromised earlier than the plasma membrane or lysosomes; and (iii) K+ extrusion possibly played a role in the final loss of cell volume. Interfering with the control of ion gradients and/or their changes in drug-treated cells resulted in cell death by necrosis.  相似文献   
63.
Mouse and human macrophages express a plasma membrane receptor for extracellular ATP named P2Z/P2X7. This molecule, recently cloned, is endowed with the intriguing property of forming an aqueous pore that allows transmembrane fluxes of hydrophylic molecules of molecular weight below 900. The physiological function of this receptor is unknown. In a previous study we reported experiments suggesting that the P2Z/P2X7 receptor is involved in the formation of macrophage-derived multinucleated giant cells (MGCs; Falzoni, S., M. Munerati, D. Ferrari, S. Spisani, S. Moretti, and F. Di Virgilio. 1995. J. Clin. Invest. 95:1207– 1216). We have selected several clones of mouse J774 macrophages that are characterized by either high or low expression of the P2Z/P2X7 receptor and named these clones P2Zhyper or P2Zhypo, respectively. P2Zhyper, but not P2Zhypo, cells grown to confluence in culture spontaneously fuse to form MGCs. As previously shown for human macrophages, fusion is inhibited by the P2Z/P2X7 blocker oxidized ATP. MGCs die shortly after fusion through a dramatic process of cytoplasmic sepimentation followed by fragmentation. These observations support our previous hypothesis that the P2Z/P2X7 receptor is involved in macrophage fusion.  相似文献   
64.
The sequence of the mitochondrial COII gene has been widely used to estimate phylogenetic relationships at different taxomonic levels across insects. We investigated the molecular evolution of the COII gene and its usefulness for reconstructing phylogenetic relationships within and among four collembolan families. The collembolan COII gene showed the lowest A + T content of all insects so far examined, confirming that the well-known A + T bias in insect mitochondrial genes tends to increase from the basal to apical orders. Fifty-seven percent of all nucleotide positions were variable and most of the third codon positions appeared free to vary. Values of genetic distance between congeneric species and between families were remarkably high; in some cases the latter were higher than divergence values between other orders of insects. The remarkably high divergence levels observed here provide evidence that collembolan taxa are quite old; divergence levels among collembolan families equaled or exceeded divergences among pterygote insect orders. Once the saturated third-codon positions (which violated stationarity of base frequencies) were removed, the COII sequences contained phylogenetic information, but the extent of that information was overestimated by parsimony methods relative to likelihood methods. In the phylogenetic analysis, consistent statistical support was obtained for the monophyly of all four genera examined, but relationships among genera/families were not well supported. Within the genus Orchesella, relationships were well resolved and agreed with allozyme data. Within the genus Isotomurus, although three pairs of populations were consistently identified, these appeared to have arisen in a burst of evolution from an earlier ancestor. Isotomurus italicus always appeared as basal and I. palustris appeared to harbor a cryptic species, corroborating allozyme data. Received: 12 January 1996 / Accepted: 10 August 1996  相似文献   
65.
Different species of the bristletail genus Lepismachilis were collected in 14 localities in Italy and Spain and an allozyme electrophoretic survey was carried out to estimate the degree of genetic variability and differentiation at intra- and interspecific levels. Four morphological species were initially identified (L osellai, L. y-signata, L. affinis, L. targionii), but the electrophoretic analysis demonstrated the presence of two additional species among the individuals of L. targionii (Lepismachilis spl and sp2). The validity of these species and their differentiation from L targionii were demonstrated by the fixation of alternative allelic patterns at several loci (7 in Lepismachilis spl and 8 in Lepismachilis sp2), coupled with fixed, previously undetected, morphological differences. In addition, Lepismachilis sp2 was sympatric with L. targionii in three collecting sites, where the fixation of alternative allelic patterns unequivocally demonstrated reproductive isolation. Genetic variability did not seem to be correlated with local ecological factors, and differences between species should rather be explained by different historical factors. Low levels of gene flow, estimated with two different indirect methods, were observed in L. targionii and L. y-signata, and were due to high levels of structuring among populations. Genetic differentiation among conspecific populations was not correlated to their geographical arrangement and the presence of loci fixed for different alleles among them suggested that stochastic factors (such as genetic drift) may have played a role in determining genetic differentiation of geographically isolated populations. Genetic divergence values indicated that the six species are well differentiated and allozyme profiles were diagnostic for all of them. On the other hand, allozyme data did not provide adequate information to resolve evolutionary relationships among the species, nor did they confirm the validity of the two subgenera (Lepismachilis and Berlesilis) in which the genus Lepismachilis is traditionally divided.  相似文献   
66.
Times of pollination of different taxa in the atmosphere of Perugia (Central Italy) over an 11-year period (1982–1992) were recorded and analysed by means of a 7-day volumetric Hirst-type pollen trap. For some taxa, the pollination period varied from year to year from a chronological and/or quantitative point of view. Several taxa showed a linkage in their starting dates of pollination. Knowledge of this kind of linkage allows us to build a forecasting model.  相似文献   
67.
The role of color and shape in the host recognition and acceptance behavior ofAphidius ervi Haliday was studied. A quantitative analysis of the oviposition behavior ofA. ervi was carried out with a computer-aided analysis of 150 video-recorded oviposition sequences on its natural host,Acyrthosiphon pisum (Harris). The importance of visual stimuli was assessed in a choice condition bioassay, observing the behavioral reaction of female parasitoids to various test materials flame-sealed into glass capillaries. Glass beads 2 and 6 mm in diameter and a flat arena were coated with cornicle secretion ofA. pisum, and their acceptance rates by both naive and experienced female parasitoids were assessed under no-choice conditions. In most cases,A. ervi females switched from random searching to attack position when the host was within a range of 1 cm, suggesting that host recognition is regulated in part by cues acting before physical contact. The glass capillary bioassay indicated that visual cues are important factors in the host recognition and acceptance phases. Pea aphid color alone can elicit the oviposition response of naiveA. ervi females, and this response is enhanced when color is combined with aphid shape. The cornicle secretion ofA. pisum stimulated an oviposition response which was stronger in naive females ofA. ervi than in experienced ones and was not significantly affected by the glass bead size or flat surface. These results, along with those from previous studies, suggest that manipulation of the oviposition behavior ofA. ervi is feasible under laboratory conditions.  相似文献   
68.
Two chlorophenyl-containing antibiotics have been isolated from a strain ofActinoplanes (ATCC 33002). Antibiotic A 15104 Y is a chlorinated phenylpyrrole compound whose structure has been confirmed by chemical synthesis. Antibiotic A 15104 Z is a chlorophenol derivative for which a structural formula is proposed on the basis of its physicochemical properties. A 15104 Y shows antimicrobial activity against Gram-positive, Gram-negative, and acid-fast bacteria, yeasts, fungi, and protozoa, while A 15104 Z possesses a low activity against Gram-positive bacteria andTrichophyton. A 15104 Y has a weak activity in curing experimentally infected mice, at a dose that is one-fifth the LD50 for the same species. This is the first example of a chloropyrrole derivative isolated from an actinomycete.  相似文献   
69.
Expression of ribosomal-protein genes in Xenopus laevis development   总被引:27,自引:0,他引:27  
Using probes to Xenopus laevis ribosomal-protein (r-protein) mRNAs, we have found that in the oocyte the accumulation of r-protein mRNAs proceeds to a maximum level, which is attained at the onset of vitellogenesis and remains stable thereafter. In the embryo, r-protein mRNA sequences are present at low levels in the cytoplasm during early cleavage (stages 2-5), become undetectable until gastrulation (stage 10) and accumulate progressively afterwards. Normalization of the amount of mRNA to cell number suggests an activation of r-protein genes around stage 10; however, a variation in mRNA turnover cannot be excluded. Newly synthesized ribosomal proteins cannot be found from early cleavage up to stage 26, with the exception of S3, L17 and L31, which are constantly made, and protein L5, which starts to be synthesized around stage 7. A complete set of ribosomal proteins is actively produced only in tailbud embryos (stages 28-32), several hours after the appearance of their mRNAs. Before stage 26 these mRNA sequences are found on subpolysomal fractions, whereas more than 50% of them are associated with polysomes at stage 31. Anucleolate mutants do not synthesize ribosomal proteins at the time when normal embryos do it very actively; nevertheless, they accumulate r-protein mRNAs.  相似文献   
70.
Rice ( Oryza sativa L.) cells returning to in vitro culture after preservation at superlow temperature in liquid nitrogen are characterized by a number of physiological alterations. These include: reduction in respiration and glucose uptake, loss of intracellular potassium, decrease in the cellular level of key metabolites (ATP, glucose-6-phosphate and pyruvate) and fragility of protoplasts following the action of cell wall-degrading enzymes.
Nevertheless, cell growth resumes after a short lag phase (2–4 days) with an actual 70–100% cell survival, thus indicating that the observed damage is not lethal and can be repaired in a short time.  相似文献   
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